The invention relates to an optical measuring head designed particularly for the surface measurement at difficult to access locations.
In the surface measuring technology tactile sensors play, as before, an important role. The measuring speed, however, is limited. Further, to the object to be measured a measuring force has to be applied which in case of sensitive surfaces, thin films or the like may lead to difficulties. Also, in tight locations the measuring force to be applied may deform the feeler element which, in case of unfavorable feeler geometries, for example, in the measuring of very deep bores, leads to uncertainties in the measurement.
Optical sensors do not have these disadvantages. The measuring speed, however, is eventually determined by the number of available photons with which a scanning of the objects without application of force is possible. It is, in principle, also feasible to detect 3D geometries. Optical sensors, however, are based on light reflected by the object, whereby numerous noise effects may appear. For example, at the edges deflection effects appear. A surface roughness may give rise to interfering speckle formation. Also, angles of inclination between the surface normals at the scanned point of the object and the optical axis of the sensor may be tolerated only to a limited extent.
For measuring bores in workpieces, for example, DE 102 56 273 A1 describes an optical line sensor, with which the wall of bores may be optically detected on an entire line. For this purpose the line sensor comprises an interferometer adjoined by an optical plate which acts as a dual prism. The light incident at one edge exits at an edge offset at 90° and is thus guided essentially perpendicularly to the wall surface.
This sensor is a special sensor which is particularly adapted for scanning surfaces which are linear in one direction, such as cylinder walls.
Further, DE 101 61 486 discloses a confocal line sensor having an object lens with several light exit windows formed as Fresnel lenses and oriented toward the workpiece. These lenses are deflection prisms to which, on the input side, optical fibers are connected. A focusing optical element is disposed between the respective optical fiber and the prism input. The prism effects a 90° deflection of light. Within the prism a parallel beam is presupposed. Such a sensor requires that the workpiece surface to be measured be oriented perpendicularly to the optical axes of the Fresnel lenses at the output side. This renders the measuring of unknown surface geometries difficult.
Accordingly, it is the object of the invention to provide a measuring head which may be used for measuring cylindrical and slightly conical bores, as well as other, difficult to access workpiece locations.